According to one embodiment, a memory system includes a memory that includes a plurality of parallel operation elements, each of which stores therein write data from a host device and on each of which read/write is individually performed, a control unit that performs the read/write to the parallel operation elements simultaneously, and a required-performance measuring unit that measures a required performance from the host device are included. The control unit changes the number of simultaneous executions of the read/write of the parallel operation elements based on the required performance measured by the required-performance measuring unit.